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INTRODUCTIONEnergy‐saving conductors are conductors with lower DC resistance than aluminium conductor steel reinforced (ACSR) with equal outside diameter, which are widely used in high‐voltage transmission lines due to their lower line loss and the ability to transmit electric power efficiently. As one of the energy‐saving conductors, aluminium conductor composite core (ACCC) conductors have the advantages of high current‐carrying capacity, low sag, corrosion resistance, and high tensile strength compared with conventional ACSR conductors, which effectively improve the power capacity of transmission lines [1]. Therefore, ACCC conductors were mainly used for the capacity improvement of transmission lines with a voltage level of 500 kV and below in service. However, the price of carbon fibre composite core conductor wires is two to three times higher than steel core aluminium stranded wires. The total length of transmission lines using ACCC conductors is more than 20,000 km globally [2]. Ultra‐high voltage (UHV) refers to AC 1000 kV, DC ± 800 kV, and above. With the rapid development of UHV projects in China, ACCC conductors are considered for use in UHV lines because of their excellent performance. The economics of the transmission line are an important basis for the selection of conductors. The economic analysis of ACCC and conventional ACSR conductors for a new UHV AC line provides guides conductor selection.The electrical, thermal, mechanical, and corrosion‐resistant qualities of the conductors are primarily responsible for the economy of ACCC conductors used in power transmission lines. ACCC conductors have been shown to have higher conductivity, higher operating temperature, lower sag, and corrosion resistance than ACSR conductors [3–8]. Therefore, ACCC conductors have lower operating losses and initial investment costs, a higher operating temperature, and a safety factor; the probability of failures during operation is smaller. However, given the economic impact, how should one choose between the ACCC and ACSR?The input–output method [9], discounted cash flow method [10], and the cost‐benefit analysis method [11] are some of the traditional economic evaluation methods used to address this issue. These methods do not consider the value of funds over time, and also ignore many factors that affect the cost of capital during the project's construction, operation, maintenance, and discard period. Deterministic (classical) methods neglect the fluctuations of energy prices; therefore, a stochastic method for power transmission design was proposed in [12]. The life cycle cost (LCC) model is now widely used in the power industry, for instance, in the economic analysis of underground cable installation [13, 14] and 500‐kV grid‐connected systems [15, 16]. Especially in the economic analysis of power transmission lines, [17, 18] provide the LCC model based on main parts of transmission line. Initial investment accounts for a large proportion of the cost of a transmission line; therefore, [19] considered the impact of many factors related to the initial investment, such as the cost of conductor, insulators, supports, and foundations. Wind speed and the icing on the sag characteristics of the conductor determine the span of the tower and the initial investment, which was carefully considered in [20]. Reference [21] pointed that the use of stranded carbon fibre cores could reduce the total investment of the project by 15%. Power transmission line loss is not only a technical index but also an economic index, [12] took the impact of line loss during operation into consideration and considered operating costs depending on conductor cross‐section and maximum line transmitted power. The corona loss was calculated by the finite difference method (FDM) method [22]. The electromagnetic loss of the conductor was determined by developing the equivalent circuit model of the transmission line [23].Although the afore‐mentioned methods accurately calculate the electromagnetic loss calculation, considering the large temperature difference between the transmission line and the surrounding environment. However, the impact of thermal radiation on the conductor temperature field needs to be considered carefully. Moreover, the LCC model used is unable to consider costs comprehensively. The LCC model, based on the initial investments, operation costs, maintenance costs, failure costs, and discard costs, precisely describes the cost of the transmission line from production, transportation, operation, and maintenance to discard. Meanwhile, a 3‐D electromagnetic–fluid–thermal coupling model based on FEM was originally proposed to calculate line loss, whose accuracy is verified by the Temperature Rise Test Platform of conductors. The main contributions to this work are summarized as follows:The multiple influencing factors are considered in the entire life cycle of the transmission lines during construction, operation, maintenance, and retirement, and the LCC of the transmission line conductor model is constructed.In terms of calculating electromagnetic loss, a 3‐D electromagnetic–fluid–thermal coupling model based on FEM was originally proposed. Compared with the experimental value originating from the Temperature Rise Test Platform of conductors, the simulation errors of the ACCC and ACSR conductors are 2.56% and 0.5%, respectively, which verifies the accuracy of the coupling‐field calculation model.The LCC model is applied in the transmission line project of the Datang‐Shengli power plant in Inner Mongolia. By considering the sag and load characteristics of the conductors, the initial investment of transmission lines is calculated. A 3‐D electromagnetic–fluid–thermal coupling model completes the calculation of an operating cost that includes electromagnetic loss. The results show that the LCC of ACCC is lower than that of ACSR, as the annual loss hours increase. When it reaches 3500 h, the overhead power transmission line with ACCC conductors saves at least 2 × 106 ¥/km when compared to ACSR.ECONOMIC EVALUATION MODEL OF CONDUCTORS IN TRANSMISSION LINEThe economic evaluation model for overhead conductors is shown in Figure 1. The initial investment cost is determined by the material and type of conductor and estimated by combining the conductor's mechanical characteristics and the transmission line cross‐sectional diagram. Maintenance and failure costs refer to the maintenance and management costs of grid staff. The operation cost of the transmission line is primarily the loss cost, which is related to the load current, atmospheric environment, regional load conditions, and conductor material. The electromagnetic–fluid–thermal coupling field is employed to calculate the resistance loss of conductors. Then the loss cost is calculated based on the annual load hours in the region. Finally, the annual sum of all costs in the entire economic operation cycle of the transmission line is determined to realize the economical evaluation of the application of ACCC conductors in transmission lines.1FIGUREOutline of the life cycle cost evaluation methodIn the design of transmission lines, different types and different materials of conductors have various electrical and mechanical properties, which affect the initial investment costs of the line (number of towers, steel consumption, additional fittings, and other consumables).LCC assessment aims to select the scheme with the lowest cost over the long term from among many schemes (13). The discount rate i is introduced to construct the transmission line LCC model of the capital investment return rate over time [24, 25].1LCC=IC+∑i=1n(OCt+MCt+FCt)1(1+t)t+DC$$\begin{equation}LCC = IC + \sum_{i = 1}^n {(O{C_t} + M{C_t} + F{C_t})} \frac{1}{{{{(1 + t)}^t}}} + DC\end{equation}$$where IC is the initial investment cost that includes the cost in the design stage, the cost of equipment procurement, and the cost of construction and installation during the construction stage. OC is an operation cost, which mainly includes the cost of equipment loss. MC is a maintenance cost, including daily maintenance, planned maintenance, and labour costs. FC is failure costs, including power loss, social impact loss etc. DC is discard cost, and t denotes the service life of an overhead transmission line.Initial costThe initial investment cost refers to the one‐time cost invested during the construction and commissioning of the line, not only to consider the purchase cost of the conductor, but also to comprehensively consider the impact of the mechanical characteristics of the conductor on the insulator, tower, and foundation. This part of the composition is very complicated and there is no standard cost model. So the engineering method to cover various costs is employed [26].2IC=nmn′ξ+∑i=1Mi$$\begin{equation}IC = nmn^{\prime}\xi + \sum_{i = 1} {{M_i}} \end{equation}$$where n is the number of conductor splits, which is set to 8, m is the conductor mass per unit length (t/km), n’ is the number of circuit loops, ξis the price per unit length, and ∑i=1Mi$\sum_{i = 1} {{M_i}} $is the sum of steel, concrete, and other expenses.Operation costOperation cost refers to the power loss cost during transmission line operation, mainly including resistance loss Qv and corona loss Pt. Resistance loss Qv is the part of electric energy converted into heat energy loss, which is caused by the current passing through the wire and the presence of wire resistance in the process of electric energy transmission in the grid, which results in the wire heating temperature rises. Moreover, AC resistance loss is caused by skin effects, iron loss, and DC resistance. Therefore, the electromagnetic loss and current‐carrying capacity of conductors are calculated by establishing the conductor electromagnetic–fluid–thermal coupling finite element model, and the accuracy of the finite element model is verified by the conductor temperature rise experimental platform [26].3OC=3n′ξ(Qv+Pk)$$\begin{equation}OC = 3n^{\prime}\xi ({Q_v} + {P_k})\end{equation}$$where n’ is the number of circuits, which is a single circuit in this paper, ξ is the transmission price, Pk is the corona loss of conductors, Qv is the electromagnetic loss of conductors, and t is the annual maximum utilization hours.Maintenance costMaintenance cost is divided into two categories: daily maintenance cost and planned maintenance cost. The daily maintenance cost of transmission lines mainly includes labour costs and additional maintenance equipment costs. The majority of the costs are accounted for by planned maintenance costs, which include the labour cost incurred in the maintenance of conductors, the maintenance of tower foundations, the replacement of insulators, and additional fittings equipment cost. According to grid industry specifications and field operation experience, the maintenance cost of a transmission line is connected to the initial investment cost, so the annual maintenance cost of the line is expressed as a percentage μ of the initial investment cost [26].4MC=μIC$$\begin{equation}MC = \mu IC\end{equation}$$Failure costEnhancing the reliability of line safe power supply has increased the line operation cost invested by power companies, but the investment in emergency backup power supply and the loss of users’ power outages have been relatively reduced. The cost of interrupted power supply loss affected by the fault is determined by various factors, including the cost of power loss and repair. In this calculation5FC=αWT+λRC·MTTR$$\begin{equation}FC = \alpha WT + \lambda RC \cdot MTTR\end{equation}$$where α is the average value of users’ interrupted power supply, W is the failure interrupt power supply (kW), T is the annual failure interruption power supply time, λis the annual average number of equipment failures, RC is the average repair cost of equipment failure, and MTTR is the average equipment repair time.Discard costDiscard cost refers to the cost of destroying and removing the line after it is scrapped. The discard cost can be positive, negative, or zero. In this calculation, the discard cost is generally estimated based on the history of the discarded line [26].6DC=IC×30%1+RI1+RAn$$\begin{equation}DC = IC \times 30\% {\left( {\frac{{1 + {R_I}}}{{1 + {R_A}}}} \right)^n}\end{equation}$$where, RI is the interest rate and RA is the inflation rate.ELECTRICAL CHARACTERISTIC ANALYSIS OF CONDUCTORSThe electrical characteristics of a conductor mainly include current‐carrying capacity and power loss. These electrical characteristics mainly affect the transmission line operating costs and the overload capacity in the event of an accident [27].The overhead conductor is in an atmospheric environment, and its operating temperature is closely related to environmental factors such as sunshine intensity, ambient temperature, and wind speed. These variables belong to the relationship of mutual coupling. Therefore, the conductor resistance loss is calculated by the electromagnetic–fluid–thermal multi‐physical coupling field analysis [28].Temperature rise test platform of conductorsDuring the operation of a transmission line, the operating temperature of the conductor is allowed to be below the maximum bearing temperature. Generally, the ACCC conductor boundary temperature is 120°C and the ACSR conductor boundary temperature is 80°C. By changing the current, the conductor temperature reaches the boundary temperature, which is the maximum current‐carrying capacity of the conductor under this environmental condition.For conducting the current‐carrying temperature rise test, only 15 m of conductors are needed. However, manufacturers only sell large‐scale, big cross‐section conductors, so we can only rely on the two types of conductors available in the laboratory (JL/G1A‐150/25 and JLRX/F1B‐150/30). Its cross‐section is shown in Figure 2.2FIGUREPhysical model of conductors. (a) JL/G1A‐150/25 and (b) JLRX/F1B‐150/30The conductor temperature rise test platform is shown in Figure 3. The two ends of the conductor are connected to the MU3248 cable ampacity test system. This instrument is used as a current generator and a monitoring platform, which can output a maximum of 2000‐A power frequency current. A multi‐point temperature measurement method is employed to measure the conductor surface temperature. The temperature in the laboratory, measured by the thermometer, is 24°C. The natural convection wind speed of the laboratory fluctuated between 0.12 and 0.17 m/s as measured by the HT9829 thermal anemometer. Through experiments, when the current‐carrying capacity of the ACCC conductor is 645 A, the conductor reaches its operating temperature of 120.1°C, and when the current‐carrying capacity of the ACSR conductor is 422 A, the conductor reaches its operating temperature of 79.8°C.3FIGURETemperature rise test platform of conductorsMultiphysics finite element modelWhen the electromagnetic–fluid–thermal coupling field simulation analysis of overhead conductors is conducted, the following assumptions need to be established:The wire model needs to be created as a three‐dimensional model using the symmetry concept. Considering that the twisted wire structures are periodic, a wire model of limited length is established for the convenience of observation. In this model, the ACSR and ACCC wires are 130 cm long.Under power frequency current (50 Hz), the eddy current field in the conductor is stable, and the influence of displacement current can be ignored.The steel core and aluminium stranded wire inside the ACSR conductor are both circular structures, with gaps between the strands, as shown in Figure 2a. Therefore, a refined ACSR conductor model is modelled to obtain more accurate data. The aluminium stranded wire of the ACCC conductor has a T‐shaped structure, which can be densely arranged. The centre comprises a round carbon fibre composite core, and the two parts are highly connected, as shown in Figure 2b. In [5, 6], when the thermal performance of the ACCC conductor is analyzed, the ACCC conductor is considered an overall cross‐section.Considering the temperature change coefficient of material resistivity, all other physical parameters are persistent.In the flow field module, the wind load is set to flow in from the right side and flow out from the left side of the air field.So only the stable temperature distribution of the conductor is considered; the time factor is ignored in the control equation.After the above assumptions about the conductor are made, according to the Maxwell equation, and the vector magnetic potential A is introduced to calculate the current distribution and electromagnetic loss of the conductor, the equations are simplified as formula (7)[29].7∇×1μ∇×A=Js−γ∂A∂t+∇φ$$\begin{equation}\nabla \times \left( {\frac{1}{\mu }\nabla \times A} \right) = {J_s} - \gamma \left( {\frac{{\partial A}}{{\partial {\rm{t}}}} + \nabla \varphi } \right)\end{equation}$$where A is the magnetic vector potential (Wb/m), φ is the electric scalar potential (V), μ is the permeability (H/m), Js${J_s}$is the current density generated by the applied electric field (A/m2), and γ is the conductivity (S/m).The overhead conductor is exposed to the atmosphere and loses some heat to the surrounding environment through radiation and convection. The following equation is used to calculate the total energy loss of the conductor due to heat convection with air [30].8Qconv=h·(Ts−Ta)$$\begin{equation}{Q_{conv}} = h \cdot ({T_s} - {T_a})\end{equation}$$where h is the convective heat transfer coefficient of the material surface, which is set to 7.37 W/m2· K [36]. Ts is the surface temperature of the conductor, and Ta is the temperature of the surrounding environment, which is set to 297 K.According to Stephen‐Boltzmann's theory, the heat flux 𝒬rad (W/m2) of radiating heat from the surface of the conductor is expressed as formula (9) [31].9Qrad=σ0ε(Ts4−Ta4)$$\begin{equation}{Q_{rad}} = {\sigma _0}\varepsilon ({T_s}^4 - {T_a}^4)\end{equation}$$where σ0 is the Stefan–Boltzmann constant (5.67 × 10−8 W/m2· °C4), and ε is the emissivity of the material at the outer surface. Simultaneously, heat gain from the sun is determined using the procedure outlined in the IEEE standard 738: 2006 (31), and its value is generally 850 to 1350 W/m2.The heat is mainly provided by the joule heat of the operating conductor. According to formula (7), the heat source 𝒬v (W/m3) in the thermal field can be expressed as formulas (10) and (11) [29]10J=∇×1μ∇×A$$\begin{equation}J = \nabla \times \frac{1}{\mu }\nabla \times A\end{equation}$$11Qv=1γJ2$$\begin{equation}{Q_v} = \frac{1}{\gamma }{\left| J \right|^2}\end{equation}$$where the conductivity of the material changes with temperature. The relationship between conductor resistance and temperature is considered linear, which is shown as follows [32]:12γT=γ201+α20(T−20)$$\begin{equation}{\gamma _T} = \frac{{{\gamma _{20}}}}{{1 + {\alpha _{20}}(T - 20)}}\end{equation}$$where α20 denotes the temperature coefficient of resistance of a conductor at 20°C, the unit is 1/°C, γT${\gamma _T}$ andγ20 denote the conductivity of the material when the temperature is T°C and 20°C, respectively, S/m.The basic electromagnetic–fluid–thermal parameters of JL/G1A‐150/25 and JLRX/F1B‐150/30 are shown in Table 1.1TABLEMaterial parameters of overhead conductorsMaterial parametersCarbon fibre core61%IACSaluminiumSteelcore63%IACSaluminiumNumber/diameter (mm)1/6.0126/2.77/2.8–Cross‐sectional area (mm2)28.26148.8624.25151.4Specific heat capacity (J/kg· °C)475880460900Thermal conductivity (W/m· °C)44.523747.2237Density (kg/m3)1600893378508933Conductivity (S/m)1 × 1033.54 × 1073.42 × 1063.65 × 107Temperature coefficient of resistance (1/°C)00.004030.00360.00407Note: 61%IACS means international annealing copper standard.Calculation of the conductor's electromagnetic loss and temperatureA calculation model is built based on the conductor temperature rise test platform as shown in Figure 3. Firstly, the geometric and material properties of the finite element model are given in Table 1. The simulation boundary conditions are set according to the laboratory environment. In the electromagnetic field, the effective value of the ACCC conductor is 645 A and the effective value of the ACSR conductor is 422 A. At the same time, the left and right sides of the air region are selected as the air inflow and outflow, and the wind speed is set to be 0.12 m/s. Finally, the ACCC and ACSR conductor model fluid fields and the conductor cross‐section thermal distribution are obtained.Since the skin effect of ACSR small radius wires is not easily resolved by COMSOL Multiphysics®, the areas where the electromagnetic field changes quickly are not analyzed well and accurate simulation results are not obtained. The edged grid of small‐radius wires should be refined along the radius. It is found that the grid is reduced in three directions of x, y, and z to a scale 10 times smaller than the original one. The result of electromagnetic loss becomes accurate. The grid diagram is shown in Figure 4.4FIGUREACSR conductor meshing diagram. ACSR, aluminium conductor steel reinforcedAs shown in Figure 5a, the electromagnetic loss at the outer layer of aluminium and steel core is unevenly distributed. The electromagnetic loss of each conductor near the inner layer is greater due to the power frequency current effect. The skin surface of the conductor produces a skin effect, which makes the current density through the inner layer of the conductor greater. The electromagnetic loss of the ACCC conductor is concentrated in the aluminium conductor part, as shown in Figure 5b, and the middle carbon fibre composite core has almost no conductivity.5FIGUREDistribution of electromagnetic losses in conductor sections. (a) JL/G1A‐150/25 type ACSR conductor, (b) JLRX/F1B‐150/30 type ACCC conductor. ACCC, aluminium conductor composite core.The flow field distribution around the JLRX/F1B‐150/30 conductor is shown in Figure 6a. The maximum temperature of the JL/G1A‐150/25 conductor is, as shown in Figure 6b, 79.4°C, which occurs at the inner layer of aluminium. The outermost aluminium strands directly heat the convection of the air exchange, and the heat dissipation rate is higher. The conductor surface temperature near the windward surface is slightly lower than that away from the windward surface and the radial temperature difference reaches 4.4°C. In this situation, the maximum allowable JL/G1A‐150/25 conductor is allowed at operating temperature. Because the conductor cross‐sections are closely arranged and the thermal conductivity of the two materials is high, the maximum temperature of the JLRX/F1B‐150/30 conductor when the wind blows over the right side of the wire is 117°C, as shown in Figure 6c. So the radial cross‐section of the ACCC conductor has almost no temperature difference.6FIGURETemperature distribution of conductor section. (a) JLRX/F1B‐150/30, (b) JL/G1A‐150/25, (c) JLRX/F1B‐150/30According to Figure 7 and Table 2, when the simulation results and the experimental results are compared, it is considered that the electromagnetic, fluid, and thermal field simulation calculation methods are correct, and there is no need to alter the simulation model.7FIGUREComparison of simulation and experimental results2TABLEComparison of simulation and experimental resultsType of conductorsCurrentExperimental resultsSimulation resultsErrorJL/G1A‐150/25422 A79.8°C79.4°C0.5%JLRX/F1B‐150/30645 A120.1°C117°C2.58%MECHANICAL ANALYSIS OF CONDUCTORSThe mechanical properties of the conductor mainly include conductor load, mechanical strength, sag characteristics, and icing overload capacity. These properties can be calculated by a single equation, including catenary function, stress–strain relations, and a tension balance equation [33].The conductor maximum sag solving flow chart is shown in Figure 8. Firstly, according to the regional meteorological conditions, safety factor K, annual average coefficient, and the relevant parameters of the conductors, the corresponding specific load wand allowable stress σ0 under each meteorological condition are calculated. Secondly, the corresponding specific loadw, temperature T, and allowable stress parameters under the four meteorological conditions that may become the stress control conditions are listed, and then the critical span length l and the control conditions are determined. According to the critical span, formulas are calculated. Finally, based on the static balance principle, the control conditions for each span length are used as the known conditions, and the meteorological conditions are used as the required conditions, yielding the horizontal stress and sag fmax for each meteorological condition [34].15fmax=wl28σ0cosβ$$\begin{equation}{f_{\max }} = \frac{{w{l^2}}}{{8{\sigma _0}\cos \beta }}\end{equation}$$8FIGUREFlow chart of solving the conductor's maximum sagwhere fmax is the maximum sag of the overhead conductor (m), w is the specific load of the overhead conductor (N), l is the line span length (m), and cosβ is the height difference angle cosine of the overhead conductor.According to the mechanical parameters of each conductor, the comparison of mechanical characteristics is calculated, as shown in Table 3.3TABLEComparison of mechanical properties of conductorsCompare itemsACSRACCCJL/G1A‐500/45JLRX1/F1A‐550/45Cross‐sectional area/mm2531.68596.56Safety factor K2.502.50Annual average operation tension limit/%2525Diameter/mm30.0028.65Unit mass/kg· m−11685.51618.8Calculate breaking force/kN127.31124.6Annual average tension/kN30.23629.593Maximum sag/mLr = 400 m12.9212.42Lr = 500 m19.2218.58Lr = 600 m27.1626.46Icing overload capacity/mmLr = 400 m26.4230.24Lr = 500 m24.2527.66Lr = 600 m22.5025.56Phase conductor maximum tension/kN241.89236.74From Table 3, the sag of the JLRX1/F1A‐550/45 conductor is smaller than the JL/G1A‐500/45 conductor. The tower height and span length are related to the sag, affecting the initial investment cost. When the span length is 500 m, the JLRX1/F1A‐550/45 conductor lowers the tower height by about 0.8 m. The ice overload capacity is about 114.6%, and is stronger than the JL/G1A‐500/45 conductor.The analysis results show that under the conditions of equal outer diameter and the same conductor tension, the sag characteristic of the ACCC conductor is almost the same as that of the ACSR conductor, so the investment cost of the iron tower is also related.ECONOMIC ANALYSIS OF ACCC CONDUCTOR IN 1000‐KV TRANSMISSION LINESIn November 2018, the construction of the new 1000‐kV transmission line project at the Shengli Station Power Plant in Inner Mongolia was completed, in which the Datang‐Xilin section project is the first 1000‐kV UHV project designed with an ACCC conductor in the world.In Table 4, two transmission lines cross the same meteorological areas. The type of conductor used in the Shenhua‐Shengli Line is a JL/G1A‐500/45 type ACSR conductor. Therefore, JL/G1A‐500/45 and JLRX/F1A‐550/45 conductors are selected for comparative analysis. The single phase of the 1000‐kV transmission line adopts an 8‐split form.4TABLETransmission lines overviewProjectDatang‐ShengliShenhua‐ShengliConductor typeACCCACSRJLRX/F1A‐550/45JL/G1A‐500/45Number of circuitsSingle circuitRated voltage1000 kVRated delivery capacity7500 MWLimit conveying capacity9000–12,000 MWLine length/km14.59118.475Straight tower number2226Tension tower number811Terrain100% flat groundMeteorological zone divisionThe basic wind speed is 30 m/s, and the design is covered with ice 10 mmCalculation of initial costAccording to the design plan of the transmission line project of the Datang‐Shengli power plant in Inner Mongolia and considering the sag and load characteristics of the two conductors, the initial investment of transmission lines is calculated. The initial investment cost of each conductor scheme is listed in Table 5.5TABLEThe ontology design scheme of transmission lines engineering ¥×104/kmCompare projectJL/G1A‐500/45JLRX1/F1A‐550/45Initial investmentcostTower300.72298.62Foundation concrete82.8480.81Foundation steel15.0514.2Conductor fittings1.282.73Conductor55.51169.25Total cost455.40565.61Agio0110.21↑24.1%All data in Table 5 are from the Inner Mongolia Electric Power Survey and Design Institute. The results show that due to the different mechanical properties of the conductors, the investment cost of the tower and the foundation investment of the ACCC conductor is lower, but the price of the ACCC conductor is about three times that of the ACSR conductor. In addition, the ACCC conductor uses a special heat‐resistant fitting, and the fitting's cost is higher. Overall, the initial investment cost of ACCC lines is 1.1021 million yuan/km higher than that of ACSR lines, about 24.1%.Calculation of operation costThe operating costs are mainly composed of labour, energy consumption, environmental protection, and other costs. Since the similar costs are still the same after conversion, it does not affect the comparison of the annual cost difference. So, the calculation of the same cost is omitted, and only the energy consumption cost is considered. The energy consumption cost is caused by the corona loss cost and the resistance loss cost.Calculation of the corona loss costThe analysis method in [35] and [36] is also applied to 1000‐kV transmission lines. When the split type and the outer diameter of the conductors are the same and they pass through the same meteorological area, the corona loss of an ACCC conductor is almost the same as an ACSR conductor. The annual cost comparison is not affected, so only the resistance loss cost is considered.Calculation of resistance loss costCalculated by the conductor electromagnetic–fluid–thermal coupling field, the current is gradually increased to reach its rated operating temperature, and the current–temperature relationship is shown in Figure 9. The current‐carrying capacity of the JLRX1/F1A‐550/45 conductor is 80% higher than that of the JL/G1A‐500/45 conductor.9FIGUREThe relationship between conductor‐carrying capacity and temperature. Note: calculation conditions: the following conditions were used in the calculation: the ambient temperature is 40°C, the wind speed is 0.5 m/s, the radiation coefficient is 0.9, the absorption coefficient is 0.9, and the sunshine intensity is 1000 W/m2The rated capacity of this line is 7500 MW, and the current in each phase line was calculated as 4558 A by Equation (16), and the current through a single conductor is 570 A.16I=Pn3Ucosα$$\begin{equation}I = \frac{P}{{n\sqrt 3 U\cos \alpha }}\end{equation}$$where n is the number of conductor splits, which is set to 8, P is the transmitting capacity (MW), I is the rated current (A), and cosα$\cos \alpha $ is the power factor, it takes 0.95 for this transmission line.As shown in Table 6, the conductor resistance loss and operating temperature at a current of 570 A are acquired by the electromagnetic–fluid–thermal coupling field analysis. The resistance loss of an ACCC conductor is about 15.54% lower than that of an ACSR conductor. In theory, this is because the ACCC wire conductivity is 4% larger than ACSR, the cross‐sectional area of ACSR is 4% larger than ACCC, and the magnetic loss in ACSR is 6% larger than ACCC, a total of 13% and 2.54% is interpreted as a simulation error.6TABLEConductor resistance lossConductors typeJL/G1A‐500/45JLRX1/F1A‐550/45Current/A570570Operation temperature/°C50.339.8Resistance loss/(W/m3)Aluminium layer3.05 × 1042.52 × 104Steel core/composite core2.5 × 1030.63Cross‐sectional area /(mm2)Aluminium layer531.68553.46Teel core/composite core43.1044.16Total resistance loss of a single conductor/(kW/km)16.3213.95The operation loss costs are closely related to the maximum utilization hours of the line load. The relationship between the maximum load utilization hours Tmax${T_{\max }}$ of the line and the loss hours τis shown in [37]. According to the power load situation in the Inner Mongolia area, when the line maximum load utilization hours are 3500 to 5500 h, the corresponding loss hours are 1600 to 3750 h. So, the operating loss cost of the line at different years of loss hours is calculated, as shown in VII.From Table 7, the loss cost of an ACCC conductor is about 35% lower than an ACSR conductor, which greatly reduces the transmission cost and CO2 emissions.7TABLESingle‐circuit power loss costsConductors typeSingle‐circuit resistance loss /(kW/km)Annual loss hours /hPower loss Q/(kWh/km)Loss cost/(¥× 104/km)8×$\;{\rm{ \times }}\;$JL/G1A‐500/45391.7816006.26 × 10525.0722008.61 × 10534.47270010.58 × 10542.31320012.54 × 10650.18375014.69 × 10658.778×JLRX1/F1A‐550/45333.3416005.33× 10521.3322007.33× 10529.3327009.00× 10536.00320010.67× 10542.67375012.50× 10550.00Note: The on‐grid electricity price is 0.4 yuan/(kW· h).Calculation of maintenance costThrough the operation and maintenance cost calculation formula (3) established in Section 2 and combined with the operation experience of UHV transmission lines, the equipment maintenance rate is 1.4%. Consequently, the maintenance cost calculation results for the two conductors are shown in Table 8. The ACCC conductor is expensive due to its special material, so the annual maintenance cost is very expensive.8TABLEMaintain cost unit:¥×104/kmConductor type8×$\; \times \;$JL/G1A‐500/458×$\; \times \;$JLRX1/F1A‐550/45Conductor cost55.51169.25MC0.782.37Calculation of failure costBased on the existing statistical data and on‐site operation experience, during the operation of UHV transmission lines, the biggest impact of fault loss is the disconnection fault, and the disconnection accident usually appears in extremely bad conditions with a very low probability. The difference between the ACCC conductor and ACSR conductor failure costs is also mainly reflected in whether there is a broken accident. The LCCs of the two types have been analyzed in this paper; only the costs of the conductors in normal operation within the service life are considered. Other failures of the two conductors during operation are almost the same, which does not affect the annual cost comparison.Calculation of discard costAccording to the power grid engineering experience, the depreciation period of overhead transmission lines is 30 years. The discard cost is calculated at 30% of the initial investment, and it is converted into an equal annual value by using macroeconomic parameter correction. Since the ACCC and ACSR conductors have the same outer diameter in this project, the difference in consumption is not large, and the final discard cost difference is small. Therefore, the discard costs of the ACCC conductor are calculated according to the ACSR conductor.In formula (4), the interest rate RI is 4.99%, and the inflation rate RA is 7.0%, so the discard costs of the two conductors are 9.37 ¥×104/km.Calculation of life cycle costThe above cost datum has been substituted into the transmission line economic evaluation model, where i is the discount rate considering the currency depreciation, which is 0.04. When the annual loss hours are 1600, 2200, 2700, 3200, and 3750 respectively, considering IC, MC, DC, and OC, the LCC models of 8 ×${\rm{ \times \;}}$JL/G1A‐500/45 and 8 ×${\rm{ \times \;}}$JLRX1/F1A‐550/45 are established as shown in Table 9:9TABLELife cycle costs unit:¥×104/kmCost itemICMCDCAnnual loss hours /hOCLCC8 × JL/G1A‐500/45455.4014.039.371600450.82929.622200619.881099.682700760.761240.573200901.651380.443750105.661535.428 × JLRX1/F1A‐550/45565.6142.619.371600383.581001.672200527.421145.002700647.291264.883200767.151384.743750899.011516.60As shown in Figure 10, when the annual loss hours are nearly 500 h, the LCC of overhead power transmission line with ACCC conductors is slightly lower than ones with ACSR, and there is little difference between them in cost, which is dominated by the more expensive price of ACCC conductors in the short term. With the increase in annual loss hours, the advantages of low electromagnetic losses of ACCC conductors are gradually emphasized. It can be seen from the LCC model that when annual loss hours reach 3500 h, an overhead power transmission line with ACCC conductors saves at least 2 × 106 ¥/km compared with ACSR. Therefore, under the condition of large annual loss hours (more than 500 h), using ACCC conductors in the UHV transmission line is undoubtedly a wise choice and will save huge expenses for the grid state.10FIGUREThe relationship between LCC and annual loss hours. LCC, life cycle costCONCLUSIONThe LCC model is taken as the quantitative evaluation standard for the economy of conductors in 1000‐kV transmission lines, in which the regional load conditions, atmospheric environment, and conductor mechanical characteristics are considered as the main variable factors affecting the LCC of a transmission line. The results show that when annual utilization hours are just over 500 h, there is minimal difference between the power transmission line using ACCC and ACSR. With increasing annual utilization hours, it is concluded that when annual loss hours reach 3500 h, an overhead power transmission line with ACCC conductors saves at least 2 × 106 ¥/km as compared to ACSR.Although the LCC of carbon fibre composite core is lower than steel core aluminium stranded wire, carbon fibre composite core conductor will cause damage during construction restricted by its mechanical properties, which will affect its service life and restrict the wide application of carbon fibre composite core conductor in practical work. Therefore, future research should concentrate on the mechanical properties and construction technology of carbon fibre composite core conductors in the future.AUTHOR CONTRIBUTIONSYujiao Zhang: Conceptualization; Funding acquisition; Methodology. Hongda Sun: Formal analysis; Software; Writing – review & editing. Xuankun zhang: Data curation; Writing – original draft. Zhiwei Chen: Investigation. li zhou: Resources. Xiongfeng Huang: Project administration; Supervision.ACKNOWLEDGEMENTSThis work is partly supported by the National Natural Science Foundation of China (52077048) and the Hubei Provincial Science Fund for Distinguished Young Scholars (No. 2019CFA085).CONFLICT OF INTERESTThe authors declare that there is no conflict of interests, and we do not have any possible conflicts of interest.DATA AVAILABILITY STATEMENTData available on request from the authors.The data that support the findings of this study are available from the corresponding author, [author initials], upon reasonable request.REFERENCESAlawar, A., Bosze, E.J., Nutt, S.R.: A composite core conductor for low sag at high temperatures. IEEE Trans. Power Deliv. 20(3), 2193–2199 (2005)Bin, L., Guangyao, Y., Xinqi, Z., et al.: Application of carbon fiber composite core conductor in new 500 KV project. Electr. 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IET Generation Transmission & Distribution – Wiley
Published: Mar 1, 2023
Keywords: energy conservation; life cycle costing; power transmission economics; ACCC conductor; energy saving; LCC; power transmission line
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